Characteristics and main controls of nano-pores in the Lower Silurian Longmaxi shale, Sichuan Basin

Abstract

The Upper Ordovician Wufeng-Lower Silurian Longmaxi shale is the only yield layer of commercial deve-lopment of shale gas in China at present. However, there are significant differences in the production of individual shale gas wells in different areas of the Sichuan Basin and its periphery. This paper investigates those differences from the perspective of reservoir space. The pore development of 36 shale samples from the Lower Rhuddanian in 5 typical wells with different reservoir pressure in different tectonic areas in the Sichuan Basin was compared by applying, petromi-neralogical, structural geological and reservoir geological methods. The reservoir space in these shales is dominated by organic pores. With the increase of TOC content, the volumes of micropores (50 nm) and total pores in different structural regions show different trends, reflecting different stages of pore evolution. A preliminary organic pore development model of shale has been established. The extent of pore development in shale samples located in the overpressure area in the basin is obviously better than that in the structural transformation area of the basin margin. It is confirmed by experiments that the shale pores may be compacted under high pressure conditions, and the degree of compaction is closely related to the organic matter pore size, the rock mineral composition, the organic matter content, the domain structure conditions and the pressure coefficient. The areas affected by the weak tectonic movement and having a high pressure coefficient are favorable areas for pore development.

Keywords

• organic matter pore
• pore development
• prediction of favorable area
• longmaxi formation
• shale
• sichuan basin